Field of the Invention
The present invention relate to wireless communication, and more particularly, to a method of transmission power control performed by a terminal in a wireless communication system, and the terminal using the method.
Related Art
Standardization works of international mobile telecommunication (IMT)-advanced which is a next generation (i.e., post 3rd generation) mobile communication system are carried out in the international telecommunication union radio communication sector (ITU-R). The IMT-advanced aims to support an Internet protocol (IP)-based multimedia service with a data transfer rate of 1 Gbps in a stationary or slowly moving state or 100 Mbps in a fast moving state.
3rd generation partnership project (3GPP) is a system standard satisfying requirements of the IMT-advanced, and prepares LTE-advanced which is an improved version of long term evolution (LTE) based on orthogonal frequency division multiple access (OFDMA)/single carrier-frequency division multiple access (SC-FDMA) transmission. The LTE-advanced (LTE-A) is one of promising candidates for the IMT-advanced.
Meanwhile, recently, there is a growing increase in a device-to-device (D2D) technique for performing direct communication between devices. In particular, the D2D is drawing attention as a communication technique for a public safety network. Although a commercial communication network is rapidly changing to LTE, the public safety network is primarily based on a 2G technique at present in terms of costs and a problem of a collision with the conventional communication protocol. Such a technical gap and a demand on an improved service results in an effort of improving the public safety network.
The public safety network has a higher service requirement (reliability and safety) in comparison with the commercial communication network, and in particular, even if cellular communication is performed in an out-of-coverage state or is not available, also demands direct signal transmission/reception between devices, i.e., a D2D operation.
The D2D operation may have various advantages in a sense that it is signal transmission/reception between proximate devices. For example, a D2D user equipment (UE) may perform data communication with a high transfer rate and a low delay. Further, the D2D operation may distribute traffic concentrated on a base station, and may have a role of extending coverage of the base station if the D2D UE plays a role of a relay.
Meanwhile, it is conventionally assumed that a terminal performs only one of a device-to-device (D2D) operation and a wide area network (WAN) operation. Herein, the WAN operation implies typical cellular communication. On the other hand, a future terminal may support that the D2D operation and the WAN operation are simultaneously performed in different carriers.
In this case, if a transmission power determination method defined under the assumption that only any one of the D2D operation and the WAN operation is performed is directly applied, as a result, a sum of transmission power for the D2D operation and transmission power for the WAN operation may be greater than maximum power that can be supported by the terminal. Therefore, there is a need for a method and apparatus for transmission power control by considering that the D2D operation and the WAN operation can be performed simultaneously in different carriers.
In addition, if transmission based on the D2D operation and WAN transmission are achieved in subframes of different carriers, there may be a case where the subframes are not temporally aligned with each other. In this case, which method will be used to determine transmission power for the transmission based on the D2D operation and the WAN transmission may be an issue to be considered.